Use of sound-pressure level in auditory distance discrimination by 6-month-old infants and adults.

Six-month-old infants have been found to respond differentially to sounding objects placed within reach and beyond reach when no visual cues were available. The goal of the present study was to investigate whether sound-pressure level (SPL) serves as an auditory cue in distance discrimination. Thirty-two 6-month-olds were presented with recordings of sounding objects first in the light at midline position, then in the dark at 45 degrees to the right and left. On half of the dark trials the object was near (15 cm), and on half it was far (100 cm). For the control group the near sound was naturally 7 dB louder than the far. The experimental group had SPL counterbalanced across near and far locations to provide an inconsistent cue. Measures of infant reaching were scored from videotape. Two groups of adults were run under similar conditions; adults were tested on reaching as well as verbal reports of distance judgment. All infants reached more for the near object, regardless of the sound's SPL, suggesting that infants did not rely on this as a major distance cue. In contrast, adults' verbal judgments of distance were based heavily on SPL, a strategy that produced higher error rates in the group with SPL counterbalanced across distance. A followup study in which adults were instructed to move their heads before judging the sound's distance did not support the hypothesis that infants' head movements were responsible for their overcoming the misleading SPL information.